Of what importance was the Westland affair?

Question

I've been reading M. Thatcher's book The_Downing_Street_Years, and she spends a lot of time discussing the Westland affair. Her account seems completely orthogonal to the one given in the Wikipedia (in fact, they seem to focus on totally different aspects of this affair).

Questions:
Why was this affair of such an importance? How was it covered in the media? Why did it pose problems at all to M.Thatcher's party? What prompted the resignations (it seems that no criminal or otherwise inappropriate activity happened at any point)?

Background
I was asked to provide more background on the Westland affair, which is hard, since I do not understand it myself. But I will try to provide some essential details nevertheless.

Thatcher's version
It has to do with the financial rescue of a British company Westland Helicopters. The principal bidder for the rescue were jointly Sikorsky and Fiat, although the British Minister of Defense, Michael Heseltine,European consortium (it is unclear, which companies were involved, and whether they were involved with the same intensity). The opposite view (as far as I udnerstand) was advocated Trade and Industry Secretary Leon Brittan. Thatcher herself claims to be neutral, but critisizes Heseltine's behavior as unethical. In the end Heseltine had resigned.

Wikipedia version
Wikipedia focuses on the scandal related with disclosure of a confidential letter, having to do with the above mentioned rescue, which led to resignation of Leon Brittan.

It is unclear why this disclosure was so damaging and whether the dispute of American-led or European takeover of the Westland was of importance (Thatcher herself mentions the rise of anti-Americanism in the wake of the affair.)

Answer 1

The actual affair was of limited importance: Should a European Consortium be given preference to take over Westland Helicopters, or a US company. How far should the government intervene in a "strategic asset".

The bigger picture is that of Cabinet discipline. The basic unwritten rule of Cabinet government is that you can argue your case in Cabinet, but once the cabinet has made a decision you support it, or quit. Until Westland, Thatcher's government had been highly united. There was plenty of criticism from her back-benchers (the "wets") but her Ministers had always closed ranks. This was the first time that a couple of senior ministers had been willing to take their dispute outside the Cabinet office and to the court of public opinion. It was the first time that ministers were being openly critical of each other, the first Cabinet split.

Hestletine resigned because he could not support the Cabinet decision (and he hoped to provoke a crisis in which he could become PM). Brittan resigned for leaking a letter to undermine Hestletine, contrary to the ministerial code.

It could have brought down the Thatcher government. The "men in dark suits"^* were meeting to decide if she retained the confidence of a sufficient number in her party. It foreshadowed the Eurosceptic/Europhile split that continues unto today.

* _{The men in dark suits. Senior members of the Conservative party. In 1975 it was they who told Edward Heath that he had to step down as Leader.}